Optical line terminal arrangement, apparatus and methods

ABSTRACT

A wavelength division multiplexed optical communication system includes a plurality of optical line terminals which may be part of separate in service networks, each having a line interface and an all-optical pass-through interface including a plurality of pass-through optical ports, and each also including a plurality of local optical ports which are connectable to client equipment and an optical multiplexer/demultiplexer for multiplexing/demultiplexing optical wavelengths. The optical multiplexer/demultiplexer may include one or more stages for inputting/outputting individual wavelengths or bands of a predetermined number of wavelengths, or a combination of bands and individual wavelengths. At least one of the pass-through optical ports of an optical line terminal of one network may be connected to at least one of the pass-through optical ports of an optical line terminal of another network to form an optical path from the line interface of the optical line terminal of the one network to the line interface of the optical line terminal of the another network to form a merged network. The use of such optical line terminals allows the upgrading and merging of the separate networks while in service.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/042,793,filed Mar. 5, 2008, which is a continuation of application Ser. No.10/737,765, filed Dec. 18, 2003, now U.S. Pat. No. 7,369,772, issued May6, 2008, which is a division of application Ser. No. 09/293,775, filedApr. 19, 1999, now U.S. Pat. No. 6,721,508, issued Apr. 13, 2004, whichclaims the benefit of U.S. Provisional Application No. 60/112,510, filedDec. 14, 1998. Each of those applications is hereby incorporated byreference in their entireties, as if fully set forth herein.

FIELD OF THE INVENTION

The invention is in the field of optical telecommunications, and moreparticularly, pertains to upgrading an in-service wavelength divisionmultiplexed (WDM) optical communication system including a pair ofoptical line terminals (OLTs) that reside in the same office and arepart of separate WDM networks to form an all optical pass-through fromthe line side of one OLT of the pair to the line side of the other OLTof the pair.

BACKGROUND OF THE INVENTION

Wavelength division multiplexing (WDM) is an approach for increasing thecapacity of existing fiber optic networks. A WDM system employs pluraloptical signal channels, each channel being assigned a particularchannel wavelength. In a WDM system optical signal channels aregenerated, multiplexed to form an optical signal comprised of theindividual optical signal channels, transmitted over a single waveguide,and demultiplexed such that each channel wavelength is individuallyrouted to a designated receiver.

SUMMARY OF THE INVENTION

In typical wavelength division multiplexing systems all wavelengths areconstrained to pass through from a source optical node to apredetermined sink optical node.

In view of the above it is an aspect of the invention to selectivelypass-through, add or drop individual wavelengths at selected opticalnodes.

It is another aspect of the invention to utilize optical line terminalshaving all-optical pass-through interfaces that provide for continuedtransmission of optical signals without any intervening electro-opticalconversion, and to connect two optical line terminals back-to-back attheir respective pass-through interfaces to provide an optical path fromthe line side interface of the first optical line terminal to the lineside interface of the second optical line terminal.

It is yet another aspect of the invention to utilize optical lineterminals having a multiplexer/demultiplexer including one or morestages for inputting/outputting individual wavelengths or bands of apredetermined number of wavelengths, or a combination of bands andindividual wavelengths.

It is a further aspect of the invention to utilize the optical lineterminals to support complex mesh network structures while permittinggrowth of an in-service network without disrupting network service.

It is yet a further aspect of the invention to provide a wavelengthdivision multiplexed optical communication system including a pluralityof optical line terminals, each having a line interface and anall-optical pass-through interface including a plurality of pass-throughoptical ports and each also including a plurality of local optical portsand an optical multiplexer/demultiplexer for multiplexing/demultiplexingtransmitted/received wavelengths. The optical multiplexer/demultiplexermay include one or more stages for inputting/outputting individualwavelengths or bands of a predetermined number of wavelengths, or acombination of bands and individual wavelengths, with at least one ofthe pass-through optical ports of one of the optical line terminalsbeing connected to at least one of the pass-through optical ports ofanother optical line terminal to form an optical path from the line sideinterface of the one of the optical line terminals to the line sideinterface of the another optical line terminal.

These and other aspects and advantages of the invention will be apparentto those of skill in the art from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an optical line terminal;

FIG. 2 is a flow chart of the control steps executed by the controller10 of FIG. 1;

FIG. 3 is a block diagram of an optical line terminal having a two-stagemultiplexer/demultiplexer;

FIG. 4 is a schematic diagram representative of the optical lineterminal of FIG. 1 or FIG. 3;

FIG. 5 is a schematic diagram of two optical line terminals such as inFIG. 4 being connected back-to-back;

FIG. 6 is a diagram illustrating how at least two separatepoint-to-point WDM systems can be upgraded while in-service to form amerged point-to-point WDM system;

FIG. 7 is a diagram illustrating how at least two separate network WDMsystems can be upgraded while in-service to form a merged network WDMsystem; and

FIG. 8 illustrates a mesh connection between a plurality of optical lineterminals.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an optical line terminal (OLT) 2 which isthe basic element of the present embodiment. The OLT 2 has aninput/output line interface 4 which is connected to an external fiberfacility and transmits/receives an optical signal having N opticalwavelengths, for example 32 wavelengths, on a single optical fiber whichis multiplexed/demultiplexed by a multiplexer/demultiplexer 6, whichoutputs demultiplexed wavelengths λ1-λN on individual optical fibers.The respective wavelengths λ1-λN are sent either to a peer OLT via apass-through port or to client equipment via a transponder and a localport. The client equipment includes SONET equipment, add/dropmultiplexers, cross-connect switches, internet protocol (IP) routers,asynchronous transfer mode switches (ATM) and the like.

As employed herein an optical signal is generally intended to encompasswavelengths in the range of approximately 300 nanometers toapproximately 2000 nanometers (UV to far IR). This range of wavelengthscan be accommodated by the preferred type of optical conductor (a fiberoptic), which typically operates in the range of approximately 800nanometers to approximately 1600 nanometers.

Consider λ1 which is provided to a 1×2 switch 8 which is controlled by acontrol signal, having at least N states, from a controller 10. Thecontroller 10 responds to a command, from a management system (notshown), at a terminal 12 to provide the control signal at a terminal 14and then to control terminal 16 of switch 8 to position the switch 8 ina first or second position. When in the first position, λ1 is providedto a transponder 18 which transmits λ1 to a client apparatus 20 via alocal port 19. When in the second position λ1 is provided to apass-through port 22 to a corresponding pass-through port in a peer OLT24. The control signal is also provided to output terminal 15, and thento control terminal 16 of a corresponding switch 8 in peer OLT 24 toroute λ1 to the corresponding multiplexer/demultiplexer 6. If it isdesired to send λ1 to both client apparatus 20 and peer OLT 24, anoptical splitter can be used in place of the switch 8.

Switch 26 selects λ1 coming from the opposite direction in response to acontrol signal at terminal 28 from controller 10 to position switch 26in a first or second position. When in the first position, 21 isreceived from client 20 via local port 19 and transponder 18, and whenin the second position 21 is received from peer OLT 24 via pass-throughport 22, and then is provided to multiplexer/demultiplex 6 to bemultiplexed with the other received wavelengths λ2-λN.

A wavelength can be directly passed-through to a peer OLT rather thanbeing sent to a client apparatus. For example, λ2 is directly sent to,and received from, peer OLT 30 via pass-through port 32.

A 1×N switch can be used to send/receive a wavelength to/from one of N-1peer OLTs or a client apparatus. For example, 1×N switch 34 undercontrol of a control signal, having at least N states, provided toterminal 36 from controller 10 sends λ3 to either peer OLT 38 viapass-through port 40, or peer OLT 42 via pass-through port 44, or peerOLT 46 via pass-through port 48 or client apparatus 50 via transponder52 and local port 53. Reception of λ3 in the opposite direction iscontrolled by N×1 switch 54 under control of a control signal providedto terminal 56 from controller 10, and than is provided tomultiplexer/demultiplexer 6 to be multiplexed with the other receivedwavelengths.

As discussed above, a wavelength can be passed-through to a peer OLT viaa pass-through port or can be optically switched to a client apparatusvia a local port. λN is shown as being directly passed through to, orreceived from, peer OLT 60 via pass-through port 62.

FIG. 2 is a flow chart of the steps performed by the controller 10 ofFIG. 1 to control the 1×2 switches 8 and 26, and the 1×N switches 34 and54 to route the respective wavelengths λ1-λN.

In step S101 the controller 10 waits for a command from a managementsystem such as a computer (not shown). At step S102 a determination ismade as to whether or not the command is a switch control signal toeither pass-through the wavelength via a pass-through port to a peer OLTor drop/add the wavelength locally at/from a client apparatus via atransponder and a local port. If the answer is no, the command ishandled by another interface (not shown) at step S103. If the answer isyes, a signal is sent to switch A (for example switch 8 or 34) to moveswitch A to transmit position X (the selected position) at step S104,and at S105 a signal is sent to switch B (for example switch 26 or 54)to move switch B to receive position X (the selected position). At step106 the control signal at terminal 15 of controller 10 is sent to thepeer OLT to set its switches A and B in a corresponding manner. Aloop-back is then made to step S101 to wait for the next command.

In the multiplexer/demultiplexer 6 of FIG. 1, 32 wavelengths on a singleoptical fiber received at line interface 4 are demultiplexed into 32individual wavelengths λ1-λ32. However, according to another aspect ofthe invention the 32 wavelengths can be demultiplexed into bands, forexample four bands of 8 wavelengths each, by a first multiplexer, andthe resultant four bands can be processed by the OLT. According toanother aspect of the invention at least one of the four bands ofwavelengths can be demultiplexed by a second multiplexer/demultiplexerinto its individual wave lengths such that the OLT can process theindividual wavelengths of the at least one band and the remaining onesof the four bands.

FIG. 3 is a block diagram illustrating a modular OLT 200 having twostages of multiplexing/demultiplexing. The operation of the OLT 200 isdescribed with respect to the demultiplexing operation; however, it isto be understood that the multiplexing is merely the reverse operation.It is to be noted that the 1×2 switches and 1×N switches shown in FIG. 1are not included in FIG. 3 in order to simplify the drawing. However, itis to be understood that in practice such switches may be utilized inthe practice of the invention. The OLT terminal 200 has an input/outputline interface 202 which is connected to an external fiber facility andreceives on a single optical fiber N, for example 32, wavelengths whichare demultiplexed by a multiplexer/demultiplexer 204, which is situatedon a first modular card, into M, for example 4, bands of 8 wavelengthseach. The first band 206 (λ1-λ8) is demultiplexed into its 8 individualwavelengths by a multiplexer/demultiplexer 208, which is situated on asecond modular card, with each such wavelength being provided to apass-through port (P) or a local port (L) via transponder (T). Each ofthe pass-through ports (P) is situated on a different modular card, andeach of the transponder (T) and its associated local port (P) aresituated together on yet another modular card. Although directconnections are shown, as discussed above the respective wavelengths maybe selectively switched to either of a local port (L) via transponder(T), or a pass-through port (P) as described with respect to FIG. 1.

The second band 210 (λ9-λ16) is provided directly to a pass-through port(P), and the third band 212 (λ17-λ24) is provided directly to apass-through port (P).

The fourth band 214 (λ25-λ32) is demultiplexed into its 8 individualwavelengths by a multiplexer/demultiplexer 216, which is situated on amodular card 217, with each such wavelength being provided to apass-through port (P) or a local port (L) via a transponder (T). Again,switching may be used to select a connection to either P or T.

FIG. 4 is a simplified schematic diagram representative of the OLT 2shown in FIG. 1 or the OLT 200 of FIG. 3. However, it is to be notedthat for simplicity only 16 wavelengths are utilized. The OLT 300interfaces and operates in a bidirectional manner as discussed in detailwith respect to FIGS. 1 and 3. The line interface 302 is adapted forwavelength division multiplexed (WDM) optical communication signals ofthe highest relative order, in this example 16 wavelengths λ1-λ16,corresponding to the N optical wavelengths on a single optical fiberwhich are applied to input/output line interfaces 4 and 202 of OLT 2(FIG. 1) and OLT 200 (FIG. 3), respectively. The pass-through interfaceconnected to the lines WL 1-4, WL 5-8, WL 9-12 and WL 13-16 correspondsto the respective pass-through ports, and the local-interface connectedto the lines labeled 16 local ports correspond to the local portsconnected to the respective transponders, where wavelengths from or toclient equipment are added or dropped.

FIG. 5 illustrates two OLTs 300A and 300B as shown in FIG. 4 connectedin a back-to-back relationship by way of their respective all-opticalpass-through interfaces. Thus, it is seen that the connection results inan optical add/drop multiplexer (OADM) functionality without requiringintermediate electro-optical conversion (OEO) of the communicatedoptical signals. As discussed above, the add/drop feature is achieved atthe 16 local ports of each OLT, where channels (wavelengths) can beadded or dropped by a manual configuration, or via add/drop switching,as controlled by switches 8 and 26 of FIG. 1, to achieve a switchableadd/drop multiplexer.

The pass-through may be accomplished using single conductors and/orribbon connectors that pass multiple individual channels (wavelengths)in one cable. The pass-through connections between OLTS 300A and 300B ispreferably made using ribbon connectors/cables.

FIG. 6 illustrates three separate in-service WDM point-to-point opticalcommunication systems A, B and C which are not initially interconnected.WDM system A includes optical nodes 400 and 402 which are opticallyconnected via their respective line interfaces, with at least opticalnode 402 being an OLT. WDM system B includes optical nodes 404 and 406which are optically connected via their respective line interfaces, withat least optical node 404 being an OLT. WDM system C includes opticalnodes 408 and 410 which are optically connected via their respectiveline interfaces, with at least optical node 408 being an OLT.

As discussed above, the three separate WDM systems are not initiallyinterconnected. However, any two of the three WDM systems, or all threeof the WDM systems, may be interconnected by connecting respective OLTsof the separate WDM system back-to-back at respective pass-through portsas shown in FIG. 5, without disrupting service. For example, WDM systemA may be connected to WDM system B by directly optically connectingpass-through ports of the OLT of node 402 to pass-through ports of theOLT of node 404 via optical fibers 416 and 418. WDM system A may also beconnected to WDM system C by directly optically connecting pass-throughoptical ports of the OLT of node 402 to pass-through ports of the OLT ofnode 408 via optical fibers 420 and 422. Thus, an all optical path isprovided from optical node 400 of WDM system A to optical node 406 ofWDM system B, and likewise an all optical path is provided from opticalnode 400 of WDM system A to optical node 410 of WDM system C, resultingin a merger of WDM systems A, B and C without disrupting service. At theback-side of the respective optical nodes, lines with a box areindicative of local ports (L) to which client equipment is normallyconnected.

FIG. 7 illustrates three separate in-service WDM network opticalcommunication systems D, E and F which are not initially interconnected.WDM system D includes optical nodes 500 and 502 which are opticallyconnected via their respective line interfaces through an opticalnetwork 503, with at least optical node 502 being an OLT. WDM system Eincludes optical nodes 504 and 506 which are optically connected viatheir respective line interfaces through an optical network 507, with atleast optical node 504 being an OLT. WDM system F includes optical nodes508 and 510 which are optically connected via their respective lineinterfaces through an optical network 511, with at least optical node508 being an OLT.

As discussed above, the three separate WDM optical networks are notinitially interconnected. However, any two of the three WDM opticalnetworks, or all three of the WDM optical networks may be interconnectedby connecting respective OLTs of the separate WDM optical networksback-to-back at respective pass-through ports as shown in FIG. 5,without disrupting service. For example, WDM optical network D may beconnected to WDM optical network E by directly optically connectingpass-through ports of the OLT of node 502 to pass-through ports of theOLT of node 504 via optical fibers 516 and 518. WDM system D may also beconnected to WDM optical network F by directly optically connectingpass-through optical ports of the OLT of node 502 to pass-through portsof the OLT of node 508 via optical fibers 520 and 522. Thus, an alloptical path is provided from optical node 500 of WDM optical network Dto optical node 506 of WDM optical network E, and likewise an alloptical path is provided from optical node 500 of WDM optical network Dto optical node 510 of WDM optical network F, resulting in a merger ofWDM network optical communication systems D, E and F without disruptingservice. At the back-side of the respective optical nodes, lines with abox are indicative of local ports (L) to which client equipment isnormally connected.

FIG. 8 illustrates how OLTs can be connected in more complex ways toachieve greater functionality, such as, for example, limitedcross-connection capabilities. Specifically, OLT 600 and OLT 602 areconnected back-to-back to form a first OADM, OLT 604 and OLT 606 areconnected back-to-back to form a second OADM, OLT 600 and OLT 606 areconnected back-to-back to form a third OADM and OLT 602 and OLT 604 areconnected back-to-back to form a fourth OADM. OLT 600, OLT 602 and OLT604 each have add/drop switching capability, whereas OLT 606 has noswitching capability.

The arrangement shown in FIG. 8 illustrates how a group of OLTs in anoffice, which may be part of separate WDM networks, can be coupled toform different OADMs on an individual channel or per band basis.Wavelengths 1, 2, 3 and 4 (channels 1, 2, 3 and 4) are connected betweenpass-through optical ports of OLT 600 and OLT 602 via optical fiber 603and are also connected between pass-through optical ports of OLT 604 andOLT 606 via optical fiber 607. Wavelengths 5, 6, 7 and 8 (channels 5, 6,7 and 8) are connected between pass-through optical ports of OLT 600 andOLT 606 via optical fiber 608 and are also connected betweenpass-through optical ports of OLT 602 and OLT 604 via optical fiber 609.Wavelengths 9, 10, 11 and 12 (channels 9, 10, 11 and 12) can beseparated into individual channels that are connected between localports of the respective OLTs. For example, channel 9 is directlyconnected between a local port of OLT 600 and a local port of OLT 602via optical fiber 610, and channel 10 is directly connected between alocal port of OLT 600 and a local port of OLT 606 via optical fiber 612.To simplify the drawing, no connections are shown for wavelengths 11 and12; however, they may be connected in a like manner. The local ports mayalso be connected to client equipment as discussed above. It is to benoted that the connection configuration of FIG. 8 does not constitute aplain patch-panel form of connectivity, insofar as it allows forswitching of channels without manual reconfigurations.

In summary, the methods and apparatus of the present invention allowupgrading of a wavelength division multiplexed optical communicationsystem including a pair of OLTs that reside in the same office orfacility and are part of separate WDM networks (whether point-to-pointlinks or more advanced networks) to form an OADM. Such upgrade isaccomplished without service disruption to the network by appropriateconnection of the OLTs through the pass-through interfaces.

Although certain embodiments of the invention have been described andillustrated herein, it will be readily apparent to those of ordinaryskill in the art that a number of modifications and substitutions can bemade to the preferred example methods and apparatus disclosed anddescribed herein without departing from the true spirit and scope of theinvention.

What is claimed is:
 1. A wavelength division multiplexed opticalcommunication system comprising: a first optical line terminal having aline interface and an all-optical pass-through interface; a secondoptical line terminal having a line interface and an all-opticalpass-through interface; and connection means for connecting theall-optical pass-through interface of said first optical line terminalto the all-optical pass-through interface of said second optical lineterminal to form an optical connection from the line side interface ofsaid first optical line terminal to the line side interface of saidsecond optical line terminal.